Almost half a billion tonnes of carbon were released from North American and Russian boreal forests in 2021, a record high and more than double the amount they emitted in 2020.
Boreal forests are high-latitude forests spanning much of Canada and Russia. They make up around a quarter of the world鈥檚 forests and store large amounts of carbon in their trees and soil.
They typically account for about 10 per cent of all carbon dioxide emissions from fires, but heatwaves in 2021 led to boreal forests contributing 23 per cent of these emissions.
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Researchers are concerned that the amount of carbon lost from boreal forests will accelerate as global temperatures rise.
鈥淭his is 20 years of warming, drought and heatwaves coming to roost and there鈥檚 no sign that it鈥檚 the end of the trend,鈥� says at the University of California, Irvine.
Satellite monitoring is commonly used to estimate the size of the area cleared by boreal forest fires, and then to estimate from that area how much carbon is released, but satellite images can miss small fires.
To measure the impact more precisely, Davis and his colleagues used satellite data on carbon monoxide in the atmosphere to estimate how much CO2 was released each year from 2020 to 2021.
They estimate that 0.48 billion tonnes of carbon were released from boreal forests in 2021, 150 per cent higher than the average yearly amount over the previous two decades.
Globally, CO2 emissions from fossil fuels and land-use change average 9 billion tonnes of carbon per year since 2000. Forest fires emit approximately 2 billion tonnes each year, while aviation contributes around tonnes.
The high number of forest fires in both North America and Russia in 2021 coincided with severe heatwaves and drought, which made the forests more flammable.
Over the past two decades, carbon emissions from boreal forest fires have risen in tandem with average temperatures.
If this trend continues, the accelerating loss of forest will release more carbon into the atmosphere, accelerating climate change and in turn making the forests more susceptible to degradation, says Davis.
Around 80 per cent of carbon lost from fires is recovered as the boreal forest regrows, but it will be less able to recover as temperatures rise and could eventually convert from being a large sink of carbon to a source.
鈥淲e鈥檙e worried that this drought and heatwave pattern that we鈥檙e seeing in the boreal areas is not abating, it鈥檚 continuing,鈥� says Davis. 鈥淢aybe this isn鈥檛 going to be a record that stands for very long.鈥�
Unlike in the Amazon rainforest, where 95 per cent of fires are started by humans, fires in the boreal region are usually natural and caused by lightning. States should do more to put them out, says Davis.
鈥淏oreal fires are causing a serious problem,鈥� says at the University of S茫o Paulo in Brazil, who wasn鈥檛 involved in the study. 鈥淣ot only in being responsible for close to half a billion tonnes of carbon 鈥� pretty much equivalent to what the Amazon loses every year through deforestation, degradations and wildfires 鈥� but also as it is reducing year after year the total area of forest, [which] is essential to remove CO2 from the atmosphere.鈥�
鈥淏oreal forest regeneration is very, very slow due to the very cold climate,鈥� he says.
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